When a semiconductor wafer is processed by a wafer processing apparatus, such as a film forming apparatus, or an etching apparatus, etc., the semiconductor wafer is positioned based on a positioning cutout portion (a notch or an ori-flat) which has been preliminary formed in a periphery of the semiconductor wafer.
The apparatus for positioning a wafer is called a pre-aligner apparatus which includes a rotary mechanism configured to hold a wafer and rotate the same, and a detecting mechanism configured to detect a cutout portion of the wafer, as basic constitution thereof. (Patent Documents 1, 2 and 3)
A wafer is transferred to or from the pre-aligner apparatus by means of, for example, a robot. This wafer transfer robot has, at the distal end of its arm, a hand adapted for holding a wafer.
A wafer carried out from a cassette by the robot is mounted on a mounting portion of the rotary mechanism of the pre-aligner apparatus and held thereon. A cutout portion of the wafer is detected by a detecting mechanism while the wafer is rotated by the rotary mechanism. Thereby, positions of the wafer in the X-Y directions and the rotational direction (θ direction) are detected. This detection operation generally requires about 3-10 seconds.
In recent years, in order to enhance the throughput of wafer processing, the time required for positioning operation by the pre-aligner apparatus is considered to be a problem.
In order to address this problem, for example, a robot is provided with two arms for transferring wafers. This robot is operated such that a wafer which has already been positioned is carried out from the rotary mechanism by one arm, and just after this, a subsequent wafer is carried to a pre-aligner apparatus by the other arm.
According to this case, comparing to the case in which a single arm is used for transferring wafers, the operational time can be reduced as a whole.
[Patent Document 1] JP2007-281249A
[Patent Document 2] JP2004-363218A
[Patent Document 3] JP2005-536878T
However, it requires a lot of costs for modifying a robot so as to increase the number of arms from one to two. Accordingly, even if the throughput of wafer processing could be enhanced, the increased costs due to the modification of the robot for providing dual arms offset the reduction effect on the costs for processing wafers.